The Science of Yawning

At approximately three o'clock Monday through Friday you have a bout with it—the stretching, open mouthed, groan of a yawn. Although yawning is a casual part of our daily lives, few know how or why we do it.

In fact, the average adult experiences about 20 yawns per day. What's most intriguing about this daily occurrence is that everyone yawns—from unborn babies to your oldest relative to your cat or dog. The question remains: Why do we yawn? What causes it? Read on to find out.

The Science

So what is a yawn? Yawning in an involuntary reflex in which the inhalation of air, the stretching of the eardrums, and lung expansion happen simultaneously. Pandiculation is the act of stretching and yawning at the same time. Other than the obvious physiological effects of yawning, the truth is that there is no definite reason as to why we do it. There are, however, many theories:

Lack of oxygen. The most common theory on yawning is to replace an oxygen deficiency in the blood. When we're bored or tired, we don't breathe as deeply as we should. So, the big gasp of air your experience while yawning forces more oxygen into the blood stream and moves carbon dioxide out.

Stretching the lungs. Another theory is that yawning stretches your lungs in order to feel more awake. The deep breath of air forces your lungs to expand and your heart rate to rise. In fact, your heart rate can rise as much as 30 percent during a yawn. The combination of increased lung capacity and heart rate may make you feel more awake.

Cooling the brain. Our brains are not unlike computers. The cooler it is the more efficient it works. The deep breath of air is said to cool an overheated brain. The brain is thought to heat up when sleep deprived or when the body is tired. Yawning counteracts those effects.

The contagious yawn. You've heard the rumor: yawns are contagious. Is there any truth to this claim? In part, yes. Fifty-five percent of people will yawn within five minutes of seeing another person yawn. A researcher at the University of Leeds in Britain believes it has to do with humans' innate empathy for "behavioral and physiological state." This theory debunks the notion that yawning in a meeting is somehow rude.

Regardless of the cause, the act of yawning is a natural part of our lives and is here to stay. Although the theories of why we yawn are disputed between sleep experts, psychologists and neighbors alike, one thing cannot be debated—the comforting feeling of a complete breath of fresh air coupled with a satisfying, full body stretch.